Sliding cam arrangement for variable actuating gas exchange valves of an internal combustion engine

ABSTRACT

A sliding cam arrangement for the variable actuation of gas exchange valves of an internal combustion engine, having a camshaft which has toothing regions with an external toothing, wherein the toothing regions mesh in each case with an internal toothing of a cam carrier, wherein the ratio of base circle radius R 2  of the cam carrier to tip circle radius R 1  of the toothing of the camshaft satisfies the following criteria: R 2/ R 1 &lt;1.55.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to German Patent Application No. 10 2012 109 690.2, filed Oct. 11, 2012, which is incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The invention relates to a sliding cam arrangement for the variable actuation of gas exchange valves of an internal combustion engine, having a camshaft which has toothing regions with an external toothing, wherein the toothing regions mesh in each case with an internal toothing of a cam carrier.

BACKGROUND OF THE INVENTION

Sliding cam arrangements of said type are well known from the prior art. For example, DE 10 2008 035 935 A1, which is incorporated by reference herein, discloses a sliding cam arrangement which has a camshaft with toothing regions, on which camshaft there are provided in each case cam carriers with two cams which engage with a respective gas exchange valve. To effect a displacement of the respective cam carrier, actuators are provided which, by means of drivers and grooves provided on the cam carriers, permit a displacement of the cam carriers in an axial direction. In the automotive field, the optimization of installation space and weight is of ever greater importance in particular against the background of increasing engine efficiency. Against this background, efforts made for the optimization of camshaft arrangements have been directed in particular to material optimization and improvements. It has nevertheless been found that the existing sliding cam arrangements have a considerable need for improvement in particular with regard to the adverse effects of the mass moment of inertia of the cam carriers.

SUMMARY OF THE INVENTION

Described herein is a sliding cam arrangement which exhibits improved dynamic behavior in an inexpensive manner which is expedient with regard to assembly.

The ratio of a base circle radius R2 of the cam carrier to a tip circle radius R1 of the toothing of the camshaft satisfies the following criteria: R2/R1<1.55. The mass inertia behavior of the sliding cam arrangement can be improved significantly in this way. Furthermore, the actuators require less power to displace the respective cam carrier, which yields an installation space reduction and cost savings with regard to the actuators too. Also, a camshaft which must possibly be produced with a relatively large diameter, because predefined spacings to the gas exchange valves must be maintained in the cylinder head, does not have an adverse effect on the overall performance of the sliding cam arrangement according to the invention. It has proven to be particularly advantageous for the ratio R2 to R1 to lie in the range from 1.2 to 1.55.

BRIEF DESCRIPTION OF THE DRAWING

The invention will be explained in more detail below on the basis of a drawing, in which:

FIG. 1 shows a top view of a sliding cam arrangement for a part of a six-cylinder V-configuration engine,

FIG. 2 shows a sectional view through a sliding cam arrangement in the region of a cam carrier according to the prior art, and

FIG. 3 shows a section through a sliding arrangement according to the invention in the region of a cam carrier.

DETAILED DESCRIPTION OF THE DRAWING

FIG. 1 shows a top view of a sliding cam arrangement 2 for one bank of a six-cylinder V-configuration engine, of which three cylinders 4 are illustrated here. In a known way, toothing regions 10 which have an external toothing 12 (in this regard, see FIGS. 2 and 3) and which mesh in each case with an internal toothing 14 of a cam carrier 16 are provided, between bearings 8, on a camshaft 6. In the present exemplary embodiment, a cam carrier is provided for two gas inlet valves (not illustrated in any more detail) and in this case has grooves 18 which interact with drivers 20 of an actuator 22 such that the respective cam carriers 16 are displaceable in the axial direction on the camshaft 6. Each cam carrier 16 also has a cam pair 24, 26 with cams 28, 30 which can in each case be placed in engagement with the associated gas exchange valve and accordingly generate a different lift characteristic of the gas exchange valve. For completeness, it is also pointed out that the component denoted by reference signs 32 is a sprocket for driving the camshaft 6.

FIG. 2 now shows a sectional view through a sliding cam arrangement 2 according to the prior art. It is possible here to clearly see the camshaft 6 on which the cam carrier 16 with the cam 30 is arranged. The camshaft has an external toothing 12 which meshes with the internal toothing 14 of the cam carrier 16. Reference 34 denotes the tip circle of the toothing. In the case of a sliding cam arrangement according to the prior art, the ratio of R2 (base circle radius) to R1 (tip circle radius of the toothing) is generally in any case >1.5, and in particular 1.6 to 1.8. It should be clear that R1 denotes the radius from the central point of the camshaft 6 to the tip circle of the external toothing 12, and R2 denotes the radius from the central point of the camshaft 6 to the base circle of the cam carrier 16.

FIG. 3 now shows the ratio of R2 to R1 in the case of the sliding cam arrangement 2 according to the invention. Here, the ratio, in the case of a corresponding base circle radius R2, is <1.55, and in the exemplary embodiment is 1.33. Even though the camshaft has a relatively high weight as a result of the increased diameter, the sliding cam arrangement 2 as a whole exhibits significantly improved dynamic behavior, wherein it was possible to realize a considerable weight saving as a result of the modified cam carriers 16. It should be clear that, where permitted by the installation-space-specific and engine-specific situation, the camshaft 6 may self-evidently also be formed with a smaller diameter, wherein an even greater weight optimization can be attained while maintaining the ratio R2 to R1. 

What is claimed:
 1. A sliding cam arrangement for variable actuation of gas exchange valves of an internal combustion engine, comprising a camshaft having toothing regions with an external toothing, wherein the toothing regions mesh with an internal toothing of a cam carrier, wherein a ratio of a base circle radius R2 of the cam carrier to a tip circle radius R1 of the toothing of the camshaft is less than 1.55.
 2. The sliding cam arrangement as claimed in claim 1, wherein the ratio is between 1.2 and 1.55. 